Currently, it is considered that integrated circuit (IC) tags are products indicating the beginning of the ubiquitous age. Labels, Suica cards, FeRAM cards, or the like have been developed previously as RF-ID (micro radio identification). Many people expect that an IC tag market will certainly grow larger in the future. However, the market has not grown enough to be expected. The reason is that there are also problems such as cost, security, and privacy other than technologies, which must be solved socially.
In addition, the RF-ID technology is considered to apply to identification of documents which have proprietary nature such as bills or securities. Forgery of bills and the like have been problems, and embedding the IC tags into the bills or the like can be devised as a method for solving those problems. However, the above-described method has not been achieved yet due to a high cost or a large size of the IC tags.
The cost of the IC tag can be reduced by reducing the size of the IC tag chip. It is because the number of IC tag chips obtained from a single wafer can be increased if the size of the IC tag chips is reduced. An IC tag chip of 0.4 millimeters square has been developed so far. This IC tag chip can read memory data of 128-bit via a 2.45 GHz microwave (refer to, for example, Non-patent Document 1).
Meanwhile, the RF-ID technology applicable to identification of bills, credit cards, or the like using components other than the IC tag is also devised. As an example thereof, a plurality of resonators which resonate to a plurality of radio frequencies are made to be contained in a substrate composed of paper or plastic in Patent Document 1. The resonator is a passive individual resonator, and resonates when a plurality of resonators are radiated by electromagnetic waves with radio frequency, and thus an arrangement of the plurality of resonators is grasped by detecting the resonance, allowing the substrate to be identified.
Patent Document 1: Japanese Unexamined Patent Publication (Kokai) No. 10-171951.
Non-patent Document 1: “Micro Radio IC Tag Chip ‘μ-Chip’” by Mitsuo Usami in Applied Physics, Vol. 73, No. 9, 2004, p.1179-p.1183.